This invention relates to radio frequency couplers and more particularly to a coupler for use with a conventional automobile receiving antenna so that such an antenna may operate with transceivers which transmit and receive rf transmissions outside the frequency band at which the antenna normally operates.
Sales of CB equipment have greatly increased in recent years, especially sales of mobile equipment such as transceivers which are installed in automobiles, recreational vehicles, trucks, etc., and which are used for two-way communications between these vehicles on and off our nation's highways. To properly use these transceivers usually necessitates the installation of an antenna on the vehicle which is specially designed for transmissions within the CB frequency range, i.e., 26.965 - 27.105 MHZ. Unfortunately, these antennas are quite distinctive in appearance and thus readily identify a vehicle on which they are installed as containing CB equipment. As a consequence, persons intent on stealing this type of radio equipment can easily spot vehicles in which they are installed and thefts of mobile CB equipment have greatly increased. Unfortunately, this equipment, once stolen, is difficult to trace and is seldom recovered by the owner.
One approach to the theft problem involves replacing the conventional receiving antenna with which most vehicles having a radio are equipped with a "disguise" antenna, i.e., an antenna that looks like a conventional receiving antenna but which is designed for CB frequency operation. While this may satisfactorily disguise the vehicle to a thief, the performance of the vehicle radio, which is not designed to operate with a CB antenna system, is greatly degraded. Consequently radio-frequency couplers have been designed for purposes of matching a radio to the CB antenna system, but while this may permit satisfactory performance to be obtained from the radio, present coupler design is such that this is accomplished with some degradation in the performance of the CB equipment. Further, the owner of the vehicle not only has the considerable expense of purchasing two separate items, but he must also have the original vehicle antenna removed, which is both a troublesome and time consuming proposition, before the new items can be installed and tested.
A second and less complicated approach retains the conventional receiving antenna already on the vehicle and requires only the addition of a radio-frequency coupler to match the radio receiver and CB equipment to the receiving antenna system. While this is also a less expensive approach than the aforementioned one, such couplers do not effect a good match between the antenna and the CB transceiver thereby reducing substantially the transfer of rf power. As a consequence, the effective range of the CB equipment is greatly diminished because of diminished signal strength and the vehicle owner is unable to realize the full potential of this equipment.